NAND type flash memory is known as a nonvolatile semiconductor memory device that is electrically rewritable and highly integrable. A NAND type flash memory includes a memory cell region in which memory cells (transistors) for storing data are arranged. A memory cell has a stacked gate structure configured by a charge accumulation layer (floating gate) and a control gate stacked on a semiconductor substrate via an insulation film.
Recently, along with progressing miniaturization of NAND type flash memory, it has become common to provide dummy cell regions near the memory cell region in order to secure margins for lithography. The dummy cell regions are necessary for forming the memory cell region to have a minimum feature size, though the dummy cell regions themselves are not formed to have a minimum feature size.
However, the stacked structure of the dummy cell regions has not yet become able to suppress deterioration of device characteristics of the memory cell region sufficiently.